CN115183696A - Forest gap characteristic measuring method in virtual forest scene - Google Patents

The invention relates to a method for measuring characteristics of a forest gap in a virtual forest scene, which comprises the following steps: s1, screening tree trunk and branch models with similar data from a model library for matching according to forest attributes, and constructing a tree three-dimensional model; s2, generating a virtual terrain according to the real terrain, and generating tree three-dimensional models with collision grids in batches in a virtual scene to realize a virtual forest window scene; and S3, measuring the forest gap characteristics through the virtual forest gap scene. The method for measuring the forest gap characteristics in the virtual forest scene overcomes the defect of difficulty in field measurement and research of the forest gap characteristics at present, provides method support for digital simulation of forestry, and provides technical support for forest gap measurement and research in the forest ecological field.

一种虚拟森林场景中林窗特征测量方法A method for measuring gap characteristics in virtual forest scene

技术领域technical field

本发明涉及林业数字化技术领域，特别涉及一种虚拟森林场景中林窗特征测量方法。The invention relates to the technical field of forestry digitization, in particular to a method for measuring gap characteristics in a virtual forest scene.

背景技术Background technique

林窗是由树木倒下等小尺度干扰或是昆虫、火灾、风雪灾等大尺度干扰引起，可以显著增强林下光照强度，从而改变森林群落组成，是森林自然更新的重要部分，目前林窗的定义还未统一，除大小外，还具有形状、有效光照辐射、立体结构等特征。在野外调查中，通常简化林窗形状，采用二维投影快速测量林窗面积，但与实际值有出入；林窗形状主要包括哑铃、椭圆、三角形等，但大多林窗并不规则，无法准确描述；林窗的三维空间结构可以通过机载激光雷达精准测量，但成本较高。而森林可视化模拟技术既可以基于实际调查数据，构建树木三维模型及其环境，真实性还原森林林窗场景；又可以通过构建大量的虚拟森林仿真环境，为林窗特征测量研究提供交互对象和平台。Forest gaps are caused by small-scale disturbances such as falling trees or large-scale disturbances such as insects, fires, wind and snow disasters, and can significantly enhance the light intensity under forests, thereby changing the composition of forest communities and are an important part of natural forest regeneration. The definition has not been unified, in addition to size, it also has the characteristics of shape, effective light radiation, three-dimensional structure and so on. In field investigation, the shape of the gap is usually simplified, and two-dimensional projection is used to quickly measure the gap area, but it is different from the actual value; the shape of gap mainly includes dumbbell, ellipse, triangle, etc., but most gaps are irregular and cannot be accurately Description; The three-dimensional spatial structure of forest gaps can be accurately measured by airborne lidar, but the cost is high. The forest visualization simulation technology can not only build a three-dimensional tree model and its environment based on the actual survey data, and restore the forest gap scene with authenticity; it can also construct a large number of virtual forest simulation environments to provide interactive objects and platforms for the measurement and research of gap characteristics. .

发明内容SUMMARY OF THE INVENTION

本发明提供一种虚拟森林场景中林窗特征测量方法，其特征在于，所述虚拟森林场景中林窗特征测量方法包括以下步骤：The present invention provides a method for measuring gap features in a virtual forest scene, characterized in that the method for measuring gap features in the virtual forest scene includes the following steps:

步骤S1，根据林木属性，从模型库中筛选数据相近的树干和树枝模型进行匹配，构建树木三维模型；Step S1, according to the attributes of the forest tree, select the trunk and branch models with similar data from the model library for matching, and construct a three-dimensional tree model;

步骤S2，依据真实地形生成虚拟地形，并在虚拟场景中批量生成带有碰撞网格的树木三维模型，实现虚拟森林林窗场景；Step S2, generating virtual terrain according to the real terrain, and generating three-dimensional tree models with collision grids in batches in the virtual scene to realize a virtual forest gap scene;

步骤S3，通过虚拟森林林窗场景对林窗特征进行测量；Step S3, measure the gap feature through the virtual forest gap scene;

所述林窗特征包括林窗边缘木、林窗大小、林窗形状和林窗立体结构；Described gap features include gap edge wood, gap size, gap shape and gap three-dimensional structure;

所述模型库包括树干模型库和树枝模型库；所述树木三维模型从树干模型库获取匹配的树高和胸径的树干三维模型，从树枝模型库获取匹配的树枝长度和倾角的树枝三维模型。The model library includes a trunk model library and a branch model library; the three-dimensional tree model obtains a matching three-dimensional trunk model of tree height and DBH from the trunk model library, and obtains a matching three-dimensional branch model of branch length and inclination angle from the branch model library.

更进一步地，在步骤S3中，林窗边缘木测量包括以下步骤：Further, in step S3, the forest gap edge wood measurement includes the following steps:

在虚拟森林林窗场景中，选择林窗内冠层高度水平面上视线开阔的点作为虚拟摄像机的位置；In the virtual forest gap scene, select a point with a wide line of sight on the canopy height level in the gap as the position of the virtual camera;

在虚拟摄像机水平方向上，以n度间隔，从0度到360度依次发射碰撞射线，碰撞到树木模型后，高亮显示该模型；In the horizontal direction of the virtual camera, the collision rays are emitted in sequence from 0 degrees to 360 degrees at intervals of n degrees. After colliding with the tree model, the model is highlighted;

记录高亮模型信息并剔除重复数据，高亮显示的树木模型即为林窗边缘木；Record the highlighted model information and remove duplicate data, and the highlighted tree model is the forest gap edge wood;

所述林窗边缘木T_{EdgeForestGap}表示为：The Gap Edge Wood T _{EdgeForestGap} is expressed as:

T_{EdgeForestGap}＝f_HighLigth(f_Camera(x，H_canopy，y))T _{EdgeForestGap} = f _HighLigth (f _Camera (x, H _canopy , y))

其中，H_canopy为林冠层高度，n^o为旋转度数间隔，f_Camera表示计算射线碰撞，f_HighLigth高亮显示碰撞树木模型，(x，H_canopy，y)表示虚拟摄像机坐标。Among them, H _canopy is the height of the forest canopy, n ^o is the rotation degree interval, f _Camera represents the calculation of the ray collision, f _HighLigth highlights the colliding tree model, and (x, H _canopy , y) represents the virtual camera coordinates.

更进一步地，在步骤S3中，林窗大小测量包括以下步骤：Further, in step S3, the gap size measurement includes the following steps:

将虚拟摄像机置于林窗上空，调整为俯视角度，以虚拟摄像机位置为空间坐标原点，沿z轴反方向发出碰撞射线，并以σ度间隔，分别绕y轴(0°，90°)扫描；Place the virtual camera above the forest gap, adjust it to the top view angle, take the virtual camera position as the origin of the spatial coordinates, emit collision rays in the opposite direction of the z-axis, and scan around the y-axis (0°, 90°) at σ degree intervals. ;

当碰撞射线与边缘木的林冠层首次碰撞，记录碰撞点坐标的三轴坐标并生成坐标点，此时记录的坐标点便是林窗边缘点；When the collision ray collides with the forest canopy of the edge tree for the first time, record the three-axis coordinates of the collision point coordinates and generate a coordinate point, and the recorded coordinate point is the forest gap edge point;

以β度间隔，绕z轴顺时针(0°，360°)旋转，重复上述步骤，最终获得(360/β)个林窗边缘点；Rotate clockwise (0°, 360°) around the z-axis at β-degree intervals, repeat the above steps, and finally obtain (360/β) gap edge points;

依次将标记点连接生成多边形，应用Shoelace Theorem公式计算林窗垂直投影面积；Connect the marked points in turn to generate a polygon, and use the Shoelace Theorem formula to calculate the vertical projected area of the forest gap;

林窗面积S表示为：The forest gap area S is expressed as:

其中，(x_i，y_i)为林窗边缘点i的垂直投影坐标，为使所有标记点形成闭合图形，定义最后一处标记点n与第一点连接，且此处计算中定义第一点的x轴坐标为x_n+1与x₁相同，y轴坐标y_n+1与y₁相同，n为总标记点数量。Among them, (x _i , y _i ) are the vertical projection coordinates of the edge point i of the forest gap. In order to make all the marked points form a closed figure, define the last marked point n to connect with the first point, and define the first point in the calculation here. The x-axis coordinate of the point is the same as x _n+1 and x ₁ , the y-axis coordinate y _n+1 is the same as y ₁ , and n is the total number of marked points.

更进一步地，在步骤S3中，林窗形状测量包括以下步骤：Further, in step S3, the forest gap shape measurement includes the following steps:

根据生成的林窗边缘标记点垂直投影坐标，连接标记点并计算周长P，应用形状指数SI表示林窗形状；According to the vertical projection coordinates of the generated gap edge marker points, connect the marker points and calculate the perimeter P, and use the shape index SI to represent the gap shape;

林窗周长P表示为：The perimeter P of the gap is expressed as:

形状指数SI表示为：The shape index SI is expressed as:

其中，P为林窗周长，(x_i，y_i)为林窗边缘点i的垂直投影坐标，为使所有标记点形成闭合图形，定义最后一处标记点n与第一点连接，且此处计算中定义第一点的x轴坐标为x_n+1与x₁相同，y轴坐标y_n+1与y₁相同，n为标记点数量，S为林窗面积。Among them, P is the perimeter of the forest gap, (x _i , y _i ) is the vertical projection coordinate of the edge point i of the forest gap, in order to make all the marked points form a closed figure, define the last marked point n to connect with the first point, and In this calculation, the x-axis coordinate of the first point is defined as x _n+1 and x ₁ , the y-axis coordinate y _n+1 is the same as y ₁ , n is the number of marked points, and S is the forest gap area.

更进一步地，在步骤S3中，林窗立体结构测量包括以下步骤：Further, in step S3, the three-dimensional structure measurement of the forest gap includes the following steps:

依次读取生成的林窗边缘点空间坐标(x_i，y_i，z_i)，将虚拟摄像机移动至与林窗边缘同一水平面且朝向林窗边缘点；Read the generated space coordinates (x _i , y _i , z _i ) of the gap edge point in turn, and move the virtual camera to the same level as the gap edge and toward the gap edge point;

以m米间隔下降直至离地1米，每次下降虚拟摄像机均向正前方发出碰撞射线，当与边缘木碰撞后，记录碰撞点坐标并生成标记点P_ij；Descend at an interval of m meters until 1 meter above the ground, and each time the virtual camera is lowered, a collision ray is sent straight ahead, and when it collides with the edge wood, the coordinates of the collision point are recorded and a marker point P _ij is generated;

生成一轮标记点后，将虚拟摄像机恢复至下一个林窗边缘点P_i+1同一水平面，绕z轴顺时针旋转β角度，此时正朝向边缘点P_i+1，重复上述操作生成新一轮标记点P_i+1j。After generating a round of marking points, restore the virtual camera to the same level of the next forest gap edge point P _i+1 , rotate β angle clockwise around the z-axis, and now it is facing the edge point P _i+1 , repeat the above operations to generate a new One round of marking points P _i+1j .

重复处理全部林窗边缘点，最终全部生成的标记点个数为((zi-1)/m))*(360/β)；将各林窗边缘点P_i与其生成标记点P_ij连接，并连接各林窗边缘点，从而形成林窗立体结构。Repeat the processing of all the gap edge points, and finally the number of all generated markers is ((zi-1)/m))*(360/β); connect each gap edge point P _i with its generated marker point P _ij , And connect the edge points of each gap to form a three-dimensional structure of gaps.

第i个林窗边缘点对应下方标记点坐标P_ij：The edge point of the i-th forest gap corresponds to the coordinate P _ij of the marked point below:

P_ij＝f_Ray(x_i，y_i，z_i-j×m)P _ij =f _Ray (x _i , y _i , z _i -j×m)

其中，(x_i，y_i，z_i)为林窗边缘点P_i坐标，j取值为(1，2，3，...，(z_i-1)/m)，j×m为摄像机下降高度，f_Ray(x_i，y_i，z_i-j×m)表示计算碰撞点坐标，即碰撞射线从虚拟摄像头(x_i，y_i，z_i-j×m)坐标出发，朝摄像头正前方与树木三维模型产生碰撞点的坐标。Among them, (x _i , y _i , z _i ) are the coordinates of the edge point P _i of the forest gap, j takes the value of (1, 2, 3, ..., (z _i -1)/m), and j×m is The falling height of the camera, f _Ray (x _i , y _i , z _i -j×m) means to calculate the coordinates of the collision point, that is, the collision ray starts from the coordinates of the virtual camera (x _i , y _i , z _i -j×m) and goes toward The coordinates of the collision point directly in front of the camera with the 3D model of the tree.

本发明达到的有益效果是：The beneficial effects achieved by the present invention are:

本发明提出一种基于虚拟森林场景测量林窗特征方法，弥补目前林窗特征野外测量研究困难的缺陷。基于模型库生成树木三维模型方法，扩展性强，适用于多种森林场景，便于推广应用，为林业数字化模拟提供方法支持。The invention proposes a method for measuring gap characteristics based on a virtual forest scene, which makes up for the defect that the current field measurement of gap features is difficult. The method of generating three-dimensional models of trees based on the model library has strong expansibility, is suitable for a variety of forest scenarios, is convenient for popularization and application, and provides method support for forestry digital simulation.

本发明基于可调节的林窗测量精度，可以快速地获取森林场景中林窗特征，便于在不同尺度的森林场景中应用，为森林生态领域林窗测量研究提供技术支撑。Based on the adjustable forest gap measurement accuracy, the invention can quickly obtain the gap characteristics in forest scenes, is convenient for application in forest scenes of different scales, and provides technical support for forest gap measurement research in the field of forest ecology.

附图说明Description of drawings

图1为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法的流程示意图；1 is a schematic flowchart of a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图2为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中林窗边缘木测量的示意图；2 is a schematic diagram of the measurement of trees at the edge of a gap in a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图3为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中林窗大小测量的示意图；3 is a schematic diagram of the size of a gap in a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图4为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中林窗立体结构测量的示意图；4 is a schematic diagram of a three-dimensional structure measurement of a gap in a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图5为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中马尾松树干三维模型的示意图；5 is a schematic diagram of a three-dimensional model of a masson pine trunk in a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图6为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中马尾松树枝三维模型的示意图；6 is a schematic diagram of a three-dimensional model of a masson pine branch in a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图7为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中虚拟马尾松林窗场景的示意图；7 is a schematic diagram of a virtual masson pine canopy scene in a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图8为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中林窗边缘木测量的示意图；8 is a schematic diagram of the measurement of trees at the edge of a gap in a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图9为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中林窗边缘点标记的示意图；9 is a schematic diagram of the edge point marking of a gap in a method for measuring gap characteristics in a virtual forest scene provided by an embodiment of the present invention;

图10为本发明实施例提供的一种虚拟森林场景中林窗特征测量方法中林窗立体结构测量的示意图。FIG. 10 is a schematic diagram of a three-dimensional structure measurement of a forest gap in a method for measuring a gap feature in a virtual forest scene provided by an embodiment of the present invention.

具体实施方式Detailed ways

下面结合附图对本发明的技术方案进行更详细的说明，本发明包括但不仅限于下述实施例。The technical solutions of the present invention will be described in more detail below with reference to the accompanying drawings. The present invention includes but is not limited to the following embodiments.

如附图1所示，本发明提出了一种虚拟森林场景中林窗特征测量方法，包括以下步骤：As shown in FIG. 1, the present invention proposes a method for measuring gap features in a virtual forest scene, comprising the following steps:

S1，根据林木属性，从模型库中筛选数据相近的树干和树枝模型进行匹配，构建树木三维模型；S1, according to the tree attributes, select the trunk and branch models with similar data from the model library for matching, and construct a three-dimensional tree model;

S2，依据真实地形生成虚拟地形，并在虚拟场景中批量生成带有碰撞网格的树木三维模型，实现虚拟森林林窗场景；S2, generate virtual terrain according to the real terrain, and generate three-dimensional tree models with collision grids in batches in the virtual scene, so as to realize the virtual forest gap scene;

S3，通过虚拟森林林窗场景对林窗特征进行测量。S3, measure the gap feature through the virtual forest gap scene.

在步骤S1中，使用SpeedTree植物建模软件，根据树种的形态结构特征，构建树木模型库。模型库包括树干模型库Trunk和树枝模型库Branch，其中树干模型库包括多个高度和胸径的树干三维模型，树枝模型库包括多个长度和倾角的树枝三维模型。In step S1, use SpeedTree plant modeling software to build a tree model library according to the morphological and structural characteristics of tree species. The model library includes a trunk model library Trunk and a branch model library Branch, wherein the trunk model library includes three-dimensional models of trunks with multiple heights and diameters at breast height, and the branch model library includes three-dimensional models of branches with multiple lengths and inclinations.

树干模型库Trunk为：The trunk model library Trunk is:

其中，H为树干高度，H_min为树干最小高度，H_max为树干最大高度，H_step为树干高度间隔；D为树干胸径，D_min为树干最小胸径，D_max为树干最大胸径，D_step为树干胸径间隔。假设有a个高度序列和b个胸径序列，则共计a×b个树干模型。Among them, H is the height of the trunk, H _min is the minimum height of the trunk, H _max is the maximum height of the trunk, H _step is the height interval of the trunk; D is the trunk diameter at breast height, D _min is the minimum trunk diameter at breast height, D _max is the maximum trunk diameter at breast height, and D _step is Trunk diameter at breast height interval. Assuming that there are a height sequences and b DBH sequences, there are a×b trunk models in total.

树枝模型库Branch：Branch model library Branch:

其中，L为树枝长度，L_min为树枝最小长度，L_max为树枝最大长度，L_step为树枝长度间隔；A为树枝倾角，A_min为树枝最小倾角，A_max为树枝最大倾角，A_step为树枝倾角间隔。假设有c个长度序列和d个倾角序列，则共计c×d个树枝模型。Among them, L is the length of the branch, L _min is the minimum length of the branch, L _max is the maximum length of the branch, L _step is the interval of the length of the branch; A is the inclination angle of the branch, A _min is the minimum inclination angle of the branch, A _max is the maximum inclination angle of the branch, and A _step is Branch inclination spacing. Assuming that there are c length sequences and d dip angle sequences, there are a total of c×d branch models.

根据林木属性，从模型库中筛选数据相近的树干和树枝模型进行匹配，从而生成符合形态构筑型的树木三维模型。According to the tree attributes, the tree trunk and branch models with similar data are selected from the model library for matching, thereby generating a three-dimensional tree model that conforms to the morphological structure.

树木三维模型Tree：Tree 3D model Tree:

其中，f(Trunk[H])和f(Trunk[D])为从树干模型库匹配获取树高H和胸径D的树干三维模型，f(Branch[L，A])为从树枝模型库匹配获取树枝长度和倾角的树枝三维模型。Among them, f(Trunk[H]) and f(Trunk[D]) are the three-dimensional models of the trunk obtained by matching the tree height H and DBH D from the trunk model library, and f(Branch[L, A]) is matching from the branch model library. Obtain a 3D model of the branch length and inclination.

在步骤S2中，虚拟森林林窗场景通过Unity3D软件构建，导入真实地形的高程灰度影像在场景中生成地形Terrain，设置地形长宽高数值从而与真实地形成比例。In step S2, the virtual forest gap scene is constructed by the Unity3D software, and the elevation grayscale image of the real terrain is imported to generate a terrain terrain in the scene, and the terrain length, width and height values are set to form a ratio with the real terrain.

地形Terrain：Terrain:

Terrain＝f(DEM，length，width，height)Terrain=f(DEM, length, width, height)

其中，DEM为地形高程数据，length为地形长度，width为地形宽度，height为地形高度。Among them, DEM is the terrain elevation data, length is the length of the terrain, width is the width of the terrain, and height is the height of the terrain.

当林木坐标未知时，可以随机生成林木坐标，或导入已知林木坐标，在虚拟场景中批量生成带有碰撞网格的林木三维模型，实现虚拟森林林窗场景。When the coordinates of the trees are unknown, the coordinates of the trees can be randomly generated, or the coordinates of the known trees can be imported, and the 3D models of trees with collision meshes can be generated in batches in the virtual scene to realize the virtual forest gap scene.

森林Forest：Forest Forest:

Forest＝f(Tree，Position，Direction)Forest=f(Tree, Position, Direction)

其中，Tree为生成的树木三维模型，Position为树木坐标，Direction为树木方向。Among them, Tree is the generated three-dimensional tree model, Position is the tree coordinates, and Direction is the tree direction.

在步骤S3中，林窗特征包括林窗边缘木、林窗大小、林窗形状和林窗立体结构。对林窗特征进行测量包括林窗边缘木测量、林窗大小测量、林窗形状测量和林窗立体结构测量。In step S3, the gap features include gap edge wood, gap size, gap shape and gap three-dimensional structure. The measurement of the gap characteristics includes the measurement of the edge of the gap, the size of the gap, the shape of the gap and the measurement of the three-dimensional structure of the gap.

林窗边缘木测量包括以下步骤：Gap edge wood measurement includes the following steps:

林窗边缘木是指包围林窗且达到林冠层高度(H_canopy)的树木，确定林窗边缘木是进行林窗形状和大小测量的前提。Gap edge wood refers to the trees that surround the gap and reach the canopy height (H _canopy ). Determining the gap edge wood is the premise for the measurement of the shape and size of the gap.

如附图2所示，在虚拟森林林窗场景中，选择林窗内冠层高度水平面上视线开阔的某一点(x，H_canopy，y)作为虚拟摄像机的位置；在虚拟摄像机水平方向上，以n度间隔，从0度到360度依次发射碰撞射线，碰撞到树木模型后，高亮显示该模型，记录高亮模型信息并剔除重复数据，此时高亮显示的树木模型便是林窗边缘木(T_{EdgeForestGap})。As shown in Figure 2, in the virtual forest gap scene, a certain point (x, H _canopy , y) with a wide line of sight on the horizontal plane of the canopy height in the gap is selected as the position of the virtual camera; in the horizontal direction of the virtual camera, At intervals of n degrees, the collision rays are emitted in sequence from 0 degrees to 360 degrees. After colliding with the tree model, the model is highlighted, the information of the highlighted model is recorded, and the duplicate data is eliminated. At this time, the highlighted tree model is the forest window. Edge wood (T _{EdgeForestGap} ).

z轴旋转角度Rz：R_z＝Rotate(0，360，n°)Z-axis rotation angle Rz: R _z =Rotate(0, 360, n°)

林窗边缘木T_{EdgeForestGap}表示为：Gap edge wood T _{EdgeForestGap} is expressed as:

T_{EdgeForestGap}＝f_HighLigth(f_Camera(x，H_canopy，y))T _{EdgeForestGap} = f _HighLigth (f _Camera (x, H _canopy , y))

其中，H_canopy为林冠层高度，n^o为旋转度数间隔，f_Camera表示计算射线碰撞，f_HighLigth高亮显示碰撞树木模型。Among them, H _canopy is the height of the forest canopy, n ^o is the rotation degree interval, f _Camera is the calculation of ray collision, and f _HighLigth highlights the collision tree model.

林窗大小测量包括以下步骤：Gap size measurement includes the following steps:

确定林窗边缘木后，隐藏非边缘木，此时虚拟森林场景内仅显示林窗边缘木。After determining the trees at the edge of the gap, hide the non-edge trees. At this time, only the trees at the edge of the gap are displayed in the virtual forest scene.

如附图3所示，将虚拟摄像机置于林窗上空，调整为俯视角度；以虚拟摄像机位置为空间坐标原点，沿z轴反方向发出碰撞射线，并以σ度间隔，分别绕y轴(0°，90°)扫描；当射线与边缘木林冠层首次碰撞，记录发生碰撞的林窗边缘点i坐标的xyz三轴坐标并生成坐标点，此时记录的坐标点便是林窗边缘点。然后以β度间隔，绕z轴顺时针(0°，360°)旋转，重复上述步骤，最终获得n(n＝360/β)个林窗边缘点。依次将边缘点连接生成多边形，应用Shoelace Theorem公式计算林窗垂直投影面积。As shown in Figure 3, the virtual camera is placed over the forest gap and adjusted to the top-down angle; the virtual camera position is used as the origin of the spatial coordinates, and the collision rays are sent out in the opposite direction of the z-axis, and are separated by σ degrees around the y-axis ( 0°, 90°) scan; when the ray collides with the marginal tree canopy for the first time, record the xyz three-axis coordinates of the i-coordinate of the gap edge point where the collision occurred and generate the coordinate point, and the recorded coordinate point at this time is the gap edge point . Then rotate clockwise (0°, 360°) around the z-axis at β degree intervals, repeat the above steps, and finally obtain n (n=360/β) gap edge points. The edge points are connected in turn to generate polygons, and the Shoelace Theorem formula is used to calculate the vertical projected area of the forest gap.

y轴旋转角度Ry：y-axis rotation angle Ry:

R_y＝Rotate(0，90，σ°)R _y =Rotate(0, 90, σ°)

z轴旋转角度Rz：Z-axis rotation angle Rz:

R_z＝Rotate(0，360，β°)R _z =Rotate(0, 360, β°)

林窗面积S表示为：The forest gap area S is expressed as:

其中，(x_i，y_i)为边缘点i的垂直投影坐标，为使所有边缘点形成闭合图形，定义最后一处边缘点n与第一点连接，且此处计算中定义第一点的x轴坐标为x_n+1与x₁相同，y轴坐标y_n+1与y₁相同，n为总边缘点数量。Among them, (x _i , y _i ) are the vertical projection coordinates of the edge point i. In order to make all the edge points form a closed graph, define the last edge point n to connect with the first point, and define the first point in the calculation here. The x-axis coordinate is the same as x _n+1 and x ₁ , the y-axis coordinate y _n+1 is the same as y ₁ , and n is the total number of edge points.

林窗形状测量包括以下步骤：Gap shape measurement includes the following steps:

根据生成的林窗边缘点垂直投影坐标，连接点并计算周长P，应用形状指数SI表示林窗形状。According to the generated vertical projection coordinates of the edge points of the gap, connect the points and calculate the perimeter P, and apply the shape index SI to express the shape of the gap.

林窗周长P：Gap perimeter P:

形状指数SI：Shape Index SI:

其中，P为林窗周长，(x_i，y_i)为边缘点i的垂直投影坐标，为使所有标记点形成闭合图形，定义最后一处边缘点n与第一点连接，且此处计算中定义第一点的x轴坐标为x_n+1与x₁相同，y轴坐标y_n+1与y₁相同，n为边缘点数量，S为林窗面积。Among them, P is the perimeter of the forest gap, (x _i , y _i ) is the vertical projection coordinate of the edge point i, in order to make all the marked points form a closed figure, define the last edge point n to connect with the first point, and here In the calculation, the x-axis coordinate of the first point is defined as xn ₊₁ and x1, the y-axis coordinate yn _{+1 is} the same as _y1 , n is the number of edge points, and S is the forest gap area.

林窗立体结构测量包括以下步骤：The three-dimensional structure measurement of the gap includes the following steps:

如附图4所示，依次读取生成的林窗边缘点P_i空间坐标(x_i，y_i，z_i)，将虚拟摄像机移动至与林窗边缘点同一水平面且朝向P_i；然后以m米间隔朝z轴下降直至离地1米，每次下降均向虚拟摄像机前方发出碰撞射线，当与边缘木碰撞后，记录碰撞点坐标并生成标记点P_ij；一轮扫描完成后，生成标记点P_ij的个数为(z_i-1)/m；将虚拟摄像机恢复至下一个林窗边缘点P_i+1同一水平面，绕z轴顺时针旋转β角度，此时正朝向边缘点P_i+1，重复上述操作生成新一轮标记点P_i+1j；最终全部生成的标记点个数为((zi-1)/m))*(360/β)；将各林窗边缘点与其生成标记点连接，并连接各林窗边缘点，从而形成林窗立体结构。As shown in accompanying drawing 4, read the space coordinates (x _i , _yi , z _i ) of the edge point P _i of the forest gap in turn, move the virtual camera to the same horizontal plane as the edge point of the forest gap and face P _i ; Descending towards the z-axis at an interval of m meters until it is 1 meter above the ground, a collision ray is sent to the front of the virtual camera each time it descends. When it collides with the edge wood, the coordinates of the collision point are recorded and the mark point P _ij is generated; after one round of scanning is completed, the generated The number of marked points P _ij is (z _i -1)/m; restore the virtual camera to the same horizontal plane as the next forest gap edge point P _i+1 , rotate β angle clockwise around the z axis, and now it is facing the edge point P _i+1 , repeat the above operation to generate a new round of marking points P _i+1j ; the number of all the marking points generated in the end is ((zi-1)/m))*(360/β); The points are connected with the generated marker points, and the edge points of each gap are connected to form a three-dimensional structure of gaps.

第i个林窗边缘点对应下方标记点坐标P_ij：The edge point of the i-th forest gap corresponds to the coordinate P _ij of the marked point below:

P_ij＝f_Ray(x_i，y_i，z_i-j×m)P _ij =f _Ray (x _i , y _i , z _i -j×m)

z轴旋转角度Rz：Z-axis rotation angle Rz:

R_z＝Rotate(0，360，β°)R _z =Rotate(0, 360, β°)

其中，(x_i，y_i，z_i)为林窗边缘点P_i坐标，j取值为(1，2，3，...，(z_i-1)/m)，j×m为摄像机下降高度，f_Ray(x_i，y_i，z_i-j×m)表示计算碰撞点坐标，即碰撞射线从虚拟摄像头(x_i，y_i，z_i-j×m)坐标出发，朝摄像头正前方与树木三维模型产生碰撞点的坐标。Among them, (x _i , y _i , z _i ) are the coordinates of the edge point P _i of the forest gap, j takes the value of (1, 2, 3, ..., (z _i -1)/m), and j×m is The falling height of the camera, f _Ray (x _i , y _i , z _i -j×m) means to calculate the coordinates of the collision point, that is, the collision ray starts from the coordinates of the virtual camera (x _i , y _i , z _i -j×m) and goes toward The coordinates of the collision point directly in front of the camera with the 3D model of the tree.

获取全部标记点P_ij坐标后，将林窗边缘点与其生成的标记点连接，并连接各林窗标记点，从而生成林窗立体结构。After obtaining the coordinates of all the marked points P _ij , connect the edge points of the forest gap with the generated marked points, and connect the marked points of each forest gap, thereby generating the three-dimensional structure of the forest gap.

具体的，以基于百山祖国家公园凤阳山保护中心提供的马尾松样地调查数据(相对坐标，树高、胸径、冠幅)共计85株为具体实施例对本发明中涉及的测量方法进行进一步说明。林木数据如表1所示。Specifically, based on the survey data (relative coordinates, tree height, DBH, crown width) of a total of 85 masson pine sample plots provided by the Fengyang Mountain Protection Center of Baishanzu National Park as a specific example, the measurement method involved in the present invention was carried out. Further explanation. The tree data are shown in Table 1.

表1林木数据Table 1 Tree data

虚拟马尾松林窗场景构建Construction of virtual masson pine tree window scene

马尾松树干模型库构建Construction of Masson Pine Trunk Model Library

基于调查数据，使用Speed Tree构建马尾松树干三维模型库，其中H_min为10m，H_max为30m，H_step为5m；D_min为5cm，D_max为35cm，D_step为5cm，共计35个树干三维模型，马尾松树干三维模型如附图5所示。Based on the survey data, Speed Tree is used to build a 3D model library of masson pine trunks, in which H _min is 10m, H _max is 30m, H _step is 5m; D _min is 5cm, D _max is 35cm, D _step is 5cm, a total of 35 trunks The three-dimensional model, the three-dimensional model of the masson pine trunk is shown in Figure 5.

树干三维模型库取值范围：The value range of the tree trunk 3D model library:

马尾松树枝模型库构建Construction of the Model Library of Masson Pine Branches

基于调查数据，使用Speed Tree软件构建马尾松树枝三维模型库，其中L_min为1.2m，L_max为4.0m，L_step为0.4m；A_min为30°，A_max为90°，A_step为10°，共计56个树枝三维模型，马尾松树干三维模型如附图6所示。Based on the survey data, a three-dimensional model library of Masson pine branches was constructed using Speed Tree software, where L _min was 1.2m, L _max was 4.0m, L _step was 0.4m; A _min was 30°, A _max was 90°, and A _step was 10°, a total of 56 three-dimensional models of branches, and the three-dimensional model of masson pine trunk is shown in Figure 6.

马尾松树枝三维模型取值范围：The value range of the 3D model of masson pine branches:

(3)虚拟马尾松森林林窗场景构建(3) Construction of the virtual masson pine forest gap scene

基于调查数据，使用Unity3D软件导入调查样地的DEM灰度影像，设置地形长度length为30m，地形宽度width为30m，地形高度为2m；根据林木属性生成马尾松三维模型，生成虚拟马尾松森林林窗场景，如附图7所示。Based on the survey data, use the Unity3D software to import the DEM grayscale image of the survey plot, set the length of the terrain as 30m, the width of the terrain as 30m, and the terrain height as 2m; generate a 3D model of Masson pine according to the tree properties, and generate a virtual masson pine forest. The window scene is shown in Figure 7.

地形Terrain：Terrain:

Terrain＝f(DEM，30m，30m，2m)Terrain=f(DEM, 30m, 30m, 2m)

虚拟马尾松林窗特征测量Characteristic measurement of virtual masson pine gaps

(1)虚拟森林场景中林窗边缘木测量(1) Wood measurement at the edge of the gap in the virtual forest scene

将虚拟摄像机放置在林窗内，以地形左下角为坐标原点，垂直高度为林冠层高度15m，水平设置为(15m，15m)，以1度间隔水平扫描森林，计算林窗边缘木，计算结果如附图8所示。Place the virtual camera in the forest gap, take the lower left corner of the terrain as the coordinate origin, the vertical height is the canopy height of 15m, and the horizontal setting is (15m, 15m), scan the forest horizontally at 1-degree intervals, and calculate the trees at the edge of the gap. As shown in Figure 8.

z轴旋转角度Rz：Z-axis rotation angle Rz:

R_z＝Rotate(0，360，1°)R _z =Rotate(0, 360, 1°)

林窗边缘木TEdgeForestGap：Gap Edge Wood TEdgeForestGap:

T_{EdgeForestGap}＝f_HighLigth(f_Camera(15m，15m，15m))T _{EdgeForestGap} = f _HighLigth (f _Camera (15m, 15m, 15m))

虚拟森林场景中林窗大小测量Gap size measurement in virtual forest scene

确定林窗边缘木后，将其他树木三维模型进行隐藏，设置摄像机离地面高度25m，摄像机坐标为(15m，12m，25m)，使摄像机俯视图覆盖林窗边缘木；y轴以1度间隔扫描，z轴以5度间隔扫描，通过上文提出的方法获取林窗边缘标记点坐标(x_i，y_i)，顺时针连接边缘点形成多边形，如附图9所示；应用Shoelace Theorem公式计算林窗面积为56.41m²。After determining the trees at the edge of the gap, hide the 3D models of other trees, set the height of the camera to 25m from the ground, and set the camera coordinates to (15m, 12m, 25m), so that the top view of the camera covers the trees at the edge of the gap; the y-axis scans at 1-degree intervals, The z-axis is scanned at 5-degree intervals, and the coordinates (x _i , y _i ) of the edge of the forest gap are obtained by the method proposed above, and the edge points are connected clockwise to form a polygon, as shown in Figure 9; the Sholace Theorem formula is used to calculate the forest gap. The window area is 56.41m ² .

y轴旋转角度Ry：y-axis rotation angle Ry:

R_y＝Rotate(0，90，1°)R _y =Rotate(0, 90, 1°)

z轴旋转角度Rz：Z-axis rotation angle Rz:

R_z＝Rotate(0，360，5°)R _z =Rotate(0, 360, 5°)

林窗面积S：Gap area S:

虚拟森林场景中林窗形状测量Gap shape measurement in virtual forest scene

根据生成的林窗边缘标记点垂直投影坐标，连接标记点计算周长P为37.73m，形状指数SI为1.42。According to the vertical projection coordinates of the generated gap edge markers, the calculated perimeter P of the connected marker points is 37.73m, and the shape index SI is 1.42.

林窗周长P：Gap perimeter P:

形状指数SI：Shape Index SI:

虚拟森林场景中林窗立体结构测量Three-dimensional structure measurement of forest gaps in virtual forest scene

根据林窗边缘点坐标，通过上文提出的方法，以1米间隔下降，以5度间隔旋转，生成标记点；连接林窗边缘点及其生成的标记点，并连接各林窗边缘点，生成马尾松林窗立体结构，如附图10所示。According to the coordinates of the gap edge points, through the method proposed above, descend at 1-meter intervals, rotate at 5-degree intervals, and generate marker points; connect the gap edge points and the generated marker points, and connect the gap edge points, The three-dimensional structure of the Masson pine gap is generated, as shown in Figure 10.

第i个林窗边缘点对应下方标记点坐标P_ij：The edge point of the i-th forest gap corresponds to the coordinate P _ij of the marked point below:

P_ij＝f_Ray(x_i，y_i，z_i-j×m)，(x_i，y_i，z_i)为林窗边缘点坐标，j取值为(1，2，3，...，(z_i-1)/m)。P _ij =f _Ray ( _xi , _yi , _zi -j×m), ( _xi , _yi , _zi ) are the coordinates of the edge of the forest gap, and j takes the value (1, 2, 3, .. ., (z _i -1)/m).

从结果可以看出，本项发明提出的一种虚拟森林场景中林窗特征测量方法具有较好的普适性，不仅可以快速测量林窗特征，而且可以选择不同的林窗特征测量精度。可以提高林业研究和相关教学的参与感和认知程度，能够满足林业数字化应用需求。It can be seen from the results that the method for measuring gap features in a virtual forest scene proposed by the present invention has good universality, and can not only quickly measure gap features, but also select different gap feature measurement accuracy. It can improve the sense of participation and cognition in forestry research and related teaching, and can meet the needs of forestry digital applications.

本发明不仅局限于上述具体实施方式，本领域一般技术人员根据实施例和附图公开内容，可以采用其它多种具体实施方式实施本发明，因此，凡是采用本发明的设计结构和思路，做一些简单的变换或更改的设计，都落入本发明保护的范围。The present invention is not limited to the above-mentioned specific embodiments. Those skilled in the art can use other various specific embodiments to implement the present invention according to the disclosed content of the embodiments and the accompanying drawings. Simple transformations or modified designs fall within the protection scope of the present invention.

1.一种虚拟森林场景中林窗特征测量方法，其特征在于，所述虚拟森林场景中林窗特征测量方法包括以下步骤：1. a method for measuring gap features in a virtual forest scene, is characterized in that, the method for measuring gap features in the virtual forest scene comprises the following steps: 步骤S1，根据林木属性，从模型库中筛选数据相近的树干和树枝模型进行匹配，构建树木三维模型；Step S1, according to the attributes of the forest tree, select the trunk and branch models with similar data from the model library for matching, and construct a three-dimensional tree model; 步骤S2，依据真实地形生成虚拟地形，并在虚拟场景中批量生成带有碰撞网格的树木三维模型，实现虚拟森林林窗场景；Step S2, generating virtual terrain according to the real terrain, and generating three-dimensional tree models with collision grids in batches in the virtual scene to realize a virtual forest gap scene; 步骤S3，通过虚拟森林林窗场景对林窗特征进行测量；Step S3, measure the gap feature through the virtual forest gap scene; 所述林窗特征包括林窗边缘木、林窗大小、林窗形状和林窗立体结构；Described gap features include gap edge wood, gap size, gap shape and gap three-dimensional structure; 所述模型库包括树干模型库和树枝模型库；所述树木三维模型从树干模型库获取匹配的树高和胸径的树干三维模型，从树枝模型库获取匹配的树枝长度和倾角的树枝三维模型。The model library includes a trunk model library and a branch model library; the three-dimensional tree model obtains a matching three-dimensional trunk model of tree height and DBH from the trunk model library, and obtains a matching three-dimensional branch model of branch length and inclination angle from the branch model library. 2.根据权利要求1所述虚拟森林场景中林窗特征测量方法，其特征在于，在步骤S3中，林窗边缘木测量包括以下步骤：2. according to the described virtual forest scene described in claim 1, the gap feature measurement method is characterized in that, in step S3, the wood gap edge measurement comprises the following steps: 在虚拟森林林窗场景中，选择林窗内冠层高度水平面上视线开阔的点作为虚拟摄像机的位置；In the virtual forest gap scene, select a point with a wide line of sight on the canopy height level in the gap as the position of the virtual camera; 在虚拟摄像机水平方向上，以n度间隔，从0度到360度依次发射碰撞射线，碰撞到树木模型后，高亮显示该模型；In the horizontal direction of the virtual camera, the collision rays are emitted in sequence from 0 degrees to 360 degrees at intervals of n degrees. After colliding with the tree model, the model is highlighted; 记录高亮模型信息并剔除重复数据，高亮显示的树木模型即为林窗边缘木；Record the highlighted model information and remove duplicate data, and the highlighted tree model is the forest gap edge wood; 所述林窗边缘木T_{EdgeForestGap}表示为：The Gap Edge Wood T _{EdgeForestGap} is expressed as: T_{EdgeForestGap}＝f_HighLigth(f_Camera(x，H_canopy，y))T _{EdgeForestGap} = f _HighLigth (f _Camera (x, H _canopy , y)) 其中，H_canopy为林冠层高度，n°为旋转度数间隔，f_Camera表示计算射线碰撞，f_HighLigth高亮显示碰撞树木模型，(x，H_canopy，y)表示虚拟摄像机坐标。Among them, H _canopy is the height of the forest canopy, n° is the rotation degree interval, f _Camera represents the calculation of ray collision, f _HighLigth highlights the colliding tree model, and (x, H _canopy , y) represents the virtual camera coordinates. 3.根据权利要求2所述虚拟森林场景中林窗特征测量方法，其特征在于，在步骤S3中，林窗大小测量包括以下步骤：3. according to the described virtual forest scene of claim 2, it is characterized in that, in step S3, the measurement of gap size comprises the following steps: 将虚拟摄像机置于林窗上空，调整为俯视角度，以虚拟摄像机位置为空间坐标原点，沿z轴反方向发出碰撞射线，并以σ度间隔，分别绕y轴(0°，90°)扫描；Place the virtual camera above the forest gap, adjust it to the top view angle, take the virtual camera position as the origin of the spatial coordinates, emit collision rays in the opposite direction of the z-axis, and scan around the y-axis (0°, 90°) at σ degree intervals. ; 当碰撞射线与边缘木的林冠层首次碰撞，记录碰撞点坐标的三轴坐标并生成坐标点，此时记录的坐标点便是林窗边缘点；When the collision ray collides with the forest canopy of the edge tree for the first time, record the three-axis coordinates of the collision point coordinates and generate a coordinate point, and the recorded coordinate point is the forest gap edge point; 以β度间隔，绕z轴顺时针(0°，360°)旋转，重复上述步骤，最终获得全部林窗边缘点；Rotate clockwise (0°, 360°) around the z-axis at β-degree intervals, repeat the above steps, and finally obtain all tree gap edge points; 依次将标记点连接生成多边形，应用Shoelace Theorem公式计算林窗垂直投影面积；Connect the marked points in turn to generate a polygon, and use the Shoelace Theorem formula to calculate the vertical projected area of the forest gap; 林窗面积S表示为：The forest gap area S is expressed as:

其中，(x_i，y_i)为林窗边缘点i的垂直投影坐标，为使所有标记点形成闭合图形，定义最后一处标记点n与第一点连接，且此处计算中定义第一点的x轴坐标为x_n+1与x₁相同，y轴坐标y_n+1与y₁相同，n为总标记点数量。Among them, (x _i , y _i ) are the vertical projection coordinates of the edge point i of the forest gap. In order to make all the marked points form a closed figure, define the last marked point n to connect with the first point, and define the first point in the calculation here. The x-axis coordinate of the point is the same as x _n+1 and x ₁ , the y-axis coordinate y _n+1 is the same as y ₁ , and n is the total number of marked points. 4.根据权利要求3所述虚拟森林场景中林窗特征测量方法，其特征在于，在步骤S3中，林窗形状测量包括以下步骤：4. according to the described virtual forest scene described in claim 3, the gap feature measurement method is characterized in that, in step S3, the gap shape measurement comprises the following steps: 根据生成的林窗边缘标记点垂直投影坐标，连接标记点并计算周长P，应用形状指数SI表示林窗形状；According to the vertical projection coordinates of the generated gap edge marker points, connect the marker points and calculate the perimeter P, and use the shape index SI to represent the gap shape; 林窗周长P表示为：The perimeter P of the gap is expressed as:

形状指数SI表示为：The shape index SI is expressed as:

其中，P为林窗周长，(x_i，y_i)为林窗边缘点i的垂直投影坐标，为使所有标记点形成闭合图形，定义最后一处标记点n与第一点连接，且此处计算中定义第一点的x轴坐标为x_n+1与x₁相同，y轴坐标y_n+1与y₁相同，n为标记点数量，S为林窗面积。Among them, P is the perimeter of the forest gap, (x _i , y _i ) is the vertical projection coordinate of the edge point i of the forest gap, in order to make all the marked points form a closed figure, define the last marked point n to connect with the first point, and In this calculation, the x-axis coordinate of the first point is defined as x _n+1 and x ₁ , the y-axis coordinate y _n+1 is the same as y ₁ , n is the number of marked points, and S is the forest gap area. 5.根据权利要求3所述虚拟森林场景中林窗特征测量方法，其特征在于，在步骤S3中，林窗立体结构测量包括以下步骤：5. according to the described virtual forest scene of claim 3, it is characterized in that, in step S3, the three-dimensional structure measurement of forest gap comprises the following steps: 依次读取生成的林窗边缘点空间坐标(x_i，y_i，z_i)，将虚拟摄像机移动至与林窗边缘同一水平面且朝向林窗边缘点；Read the generated space coordinates (x _i , y _i , z _i ) of the gap edge point in turn, and move the virtual camera to the same level as the gap edge and toward the gap edge point; 以m米间隔下降直至离地1米，每次下降虚拟摄像机均向林窗边缘点发出碰撞射线，当与边缘木碰撞后，记录碰撞点坐标并生成标记点P_ij；Descend at an interval of m meters until 1 meter above the ground, and each time the virtual camera descends, a collision ray is sent to the edge point of the forest gap, and after colliding with the edge wood, the coordinates of the collision point are recorded and the mark point P _ij is generated; 生成一轮标记点后，将虚拟摄像机恢复至下一个林窗边缘点P_i+1同一水平面，绕z轴顺时针旋转β角度，此时正朝向边缘点P_i+1，重复上述操作生成新一轮标记点P_i+1j；After generating a round of marking points, restore the virtual camera to the same level of the next forest gap edge point P _i+1 , rotate β angle clockwise around the z-axis, and now it is facing the edge point P _i+1 , repeat the above operations to generate a new One round of marking points P _i+1j ; 重复处理全部林窗边缘点，最终全部生成的标记点个数为((zi-1)/m))*(360/β)；将各林窗边缘点P_i与其生成标记点P_ij连接，并连接各林窗边缘点，从而形成林窗立体结构；Repeat the processing of all the gap edge points, and finally the number of all generated markers is ((zi-1)/m))*(360/β); connect each gap edge point P _i with its generated marker point P _ij , And connect the edge points of each gap to form a three-dimensional structure of gaps; 林窗边缘标记点i对应下方标记点坐标P_ij：The marker point i on the edge of the forest gap corresponds to the coordinates P _ij of the lower marker point: P_ij＝f_Ray(x_i，y_i，z_i-j×m)P _ij =f _Ray (x _i , y _i , z _i -j×m) 其中，(x_i，y_i，z_i)为林窗边缘点P_i坐标，j取值为(1，2，3，...，(z_i-1)/m)，j×m为摄像机下降高度，f_Ray(x_i，y_i，z_i-j×m)表示计算碰撞点坐标，即碰撞射线从虚拟摄像头(x_i，y_i，z_i-j×m)坐标出发，朝摄像头正前方与树木三维模型产生碰撞点的坐标。Among them, (x _i , y _i , z _i ) are the coordinates of the edge point P _i of the forest gap, j takes the value of (1, 2, 3, ..., (z _i -1)/m), and j×m is The falling height of the camera, f _Ray (x _i , y _i , z _i -j×m) means to calculate the coordinates of the collision point, that is, the collision ray starts from the coordinates of the virtual camera (x _i , y _i , z _i -j×m) and goes toward The coordinates of the collision point directly in front of the camera with the 3D model of the tree.